I think the reason why they chose the Soviet/Communist partisans is because they were the most active resistance groups in WW2. If I remember correctly Soviet partisans was large (90,000 by 1941 and 500,000 in 1942) and were extremely effective as a fighting force that they even had their own dedicated aviation unit (101st Long Range Aviation Regiment).
I think the reason why they chose the Soviet/Communist partisans is because they were the most active resistance groups in WW2. If I remember correctly Soviet partisans was large (90,000 by 1941 and 500,000 in 1942) and were extremely effective as a fighting force that they even had their own dedicated aviation unit (101st Long Range Aviation Regiment).